1. Field of the Invention
This invention relates to an adhesive which is prepared by copolymerizing two vinyl compounds, compound (1) containing an aziridinyl group and the other usually consisting of an acrylic acid ester or a methacrylic acid ester of an alcohol having from 1 to 8 carbon atoms per molecule.
2. Description of the Prior Art
In recent times, there has been significant use of polyvinyl fluoride sheets in laminated structures which, for example, are used as wall covering materials because they have superior weather resistance, wear resistance, and resistance to solvents. The polyvinyl fluoride sheets are marketed under the trademark "Tedlar" by E. I. du Pont de Nemours & Co. In this type of polyvinyl fluoride polymer, one hydrogen atom is substituted by one fluorine atom in each ethylene unit of the polyethylene.
An adhesive to be suitable for use in attaching "Tedlar" film or sheet to the surface of a metal such as aluminum or to a polyvinyl chloride article must have various requirements, for example, high adhesiveness, high cohesiveness, a stability to hydrolysis and the like. If the adhesive does not meet these requirements, the film or sheet is apt to be peeled away from the surface of the metal and the polyvinyl fluoride could not be effectively used in the laminate.
Adhesives for "Tedlar" films or sheets are disclosed in Japanese Patent Publication No. 18530/1963 (corresponding to U.S. Pat. No. 3,133,854), No. 26763/1963 and No. 11918/1967 by E. I. du Pont de Nemours & Co. These adhesives are manufactured in a process in which one or more types of acrylates or methacrylates are copolymerized with a small amount of a monomer having an epoxy group, and gaseous ammonia or a primary monoamine are reacted with the resulting copolymer. The adhesive thus obtained consists of an acrylate or methacrylate polymer having an amino group or an imino group on the side chain.
The "Tedlar" film to be attached to the substrate may be surface treated in a special manner as described in Japanese Patent Publications Nos. 18530/1963 and 11918/1967. We have investigated the adhesive properties of the surface treated "Tedlar" produced according to these disclosures. A methacrylic polymer having a carboxyl group, a hydroxyl group, an amide group, or a carbonyl group as the functional groups on the side chain exhibited little adhesiveness toward "Tedlar". A methacrylic polymer having glycidyl groups on the side chain exhibited some adhesiveness to the "Tedlar". However, this adhesiveness was not particularly satisfactory.
The methacrylic polymer of the Japanese patents has the following functional group: ##STR2## where Z is a hydrocarbon group, and R.sub.1, R.sub.2 and R.sub.3 are alkyl groups, respectively. Such a polymer is synthesized by the reaction of amines with a vinyl polymer including glycidyl methacrylate and the like, or by reaction of imines with a vinyl polymer of a carboxylic acid. However, these known adhesives have the disadvantage that they require a large number of steps in the synthesis and also that the imines are strongly toxic and have carcinogenic properties.